1. Field of the Invention
The present invention relates to a print color material amount determining method for an image binarization apparatus used to output a color image in a color printing press, a color printer, a color copying machine, a color facsimile system, and the like and, more particularly, to a method of determining the amounts of print color materials including a black color material from information recorded by color representation based on a uniform color space.
2. Description of the Related Art
In a conventional color printing scheme, a conventional color printer, and the like, three small dots of three colors, i.e., cyan (C), magenta (M), and yellow (Y), or four small dots including a dot of black (K) are superposed on each other by a stochastic method, and an arbitrary color is generated as the average of these colors. In an image editing apparatus used in such a field of printing techniques, values proportional to the dot areas of C, M, Y, and K are used as values representing colors. In general, these CMY values or CMYK values can be obtained by a color scanner for printing.
In recent years, a color printer, a color copying machine, or the like is sometimes connected to an image editing apparatus to obtain a proof for checking the colors of reproduced images. Such image reproduction mechanisms are based on various printing schemes such as electrophotography, a dye diffusion thermal transfer scheme, and an ink-jet printing scheme. Color materials used for an image reproduction mechanism include various types of pigments and dyes.
In general, an output unit used for such an image reproduction mechanism is designed to receive CMY values, CMYK values, or RGB (red, green, and blue) signals and reproduce an image on the basis of these values. However, such CMY values, CMYK values, and RGB values are dependent on the type of unit. For this reason, an image reproduced by the output unit of this image reproduction mechanism is affected by the above printing scheme employed by the image reproduction mechanism and the type of pigment or dye used in the image reproduction mechanism. That is, even if signals (CMY values, CMYK values, or RGB values) of the same values are input to output units, the colors of reproduced images differ from each other depending on the types of output units or the types of color materials used. Therefore, it is difficult to obtain the same colors on printed matters by simply transferring RGB values, obtained by subtracting CMY values from the maximum values, to output units such as a color printer and a color copying machine, because of the above-described differences in the types of image reproduction mechanisms and color materials.
In order to solve such a problem, values independent of the characteristics of an output unit may be used as color representation values instead of the above CMYK values. For example, values based on the CIE L*u*v* system and the CIE L*a*b* system as uniform color spaces which are the color systems specified by Commission Internationale de l'Eclairage (CIE) are values independent of the characteristics of an output unit. Therefore, values independent of the characteristics of an output unit, e.g., CIE L*a*b values, are used in an image editing apparatus. When values are to be output to various types of output units, CIE L*a*b* values are converted into CMY values, CMYK values, or RGB values representing the amounts of print color materials which are independent of the characteristics of the respective output units.
As methods of converting CIE L*a*b* values or CIE L*u*v* values into CMY values or RGB values representing the amounts of color materials which are independent of the characteristics of the respective output units, a least squares method, an interpolated look-up table (LUT) method, and a method using a neural network are known.
In general, CIE L*a*b* or CIE L*u*v values based on uniform color spaces are three-dimensional information, whereas CMYK values are four-dimensional information. For this reason, it is difficult to convert CIE L*a*b* or CIE L*u*v values into CMYK values as four-dimensional information, although these values can be converted into three-dimensional information such as CMY or RGB values by using the least squares method, the interpolated look-up table method, the neural network method, or the like.